Introducer sheath having profiled reinforcing member

ABSTRACT

An introducer sheath includes an inner liner having a passageway extending longitudinally therethrough, a coil positioned over the inner liner, and an outer jacket positioned over the liner and the coil. The outer jacket is bonded to the inner liner between the coil turns. The coil turns have a cross-section comprising opposing end portions, and a center portion disposed between the opposing end portions. The center portion has a thickness not exceeding about one-third of a thickness of the end portions for reducing a bending modulus of the coil, and the end portions have a generally curved outer surface. At least a distal end portion of the outer jacket has a durometer between about 70 and 90 on the Shore D scale.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of U.S. application Ser. No.13/569,487, filed Aug. 8, 2012, entitled “INTRODUCER SHEATH HAVINGPROFILED REINFORCING MEMBER,” the entire contents of which areincorporated herein by reference.

FIELD OF THE INVENTION

This invention relates to the field of medical devices, and moreparticularly, to an introducer sheath having a reinforcing memberprofiled for enhancing the flexibility of the sheath.

BACKGROUND OF THE INVENTION

Numerous advances of considerable note have occurred in medical surgicaltechniques over the last few decades. Among the most significantadvances has been the adoption, and now-routine performance, of a widevariety of minimally invasive procedures. When carrying out suchprocedures, access to a site of concern within a patient is achievedthrough a relatively small incision, into which a tubular device (suchas a sheath) is inserted or introduced. The sheath keeps the incisionopen while permitting access to the target site via the interior (i.e.,lumen) of the sheath. Non-limiting examples of such devices includeintroducer sheaths, guide catheters, and like devices (devicescollectively referred to herein as “sheaths” or “introducer sheaths”).

Body passageways in which medical interventional devices, such asstents, are now commonly introduced include the esophagus, trachea,colon, biliary tract, urinary tract, and vascular system, among otherlocations within the body. When placing a medical interventional devicein a passageway, communication with the passageway is typically attainedby initially inserting the distal end of the introducer sheath into thebody passageway. Since the introducer sheath must often traversetortuous passageways to reach the target site, the sheath often includesa coil reinforcement to enhance the flexibility of the sheath, andthereby, facilitate passage of the sheath through the passageway withoutkinking. Examples of introducer sheaths of this type are described inU.S. Pat. No. 5,380,304, and U.S. Pat. Publ. No. 2001/0034514, bothincorporated by reference herein.

The sheaths described in these patent documents include a lubriciousinner liner and a helical coil fitted over the liner. The coil istypically formed from flat wire, i.e., wire having a substantiallyrectangular cross-section. Utilizing a flat wire coil enables the sheathto maintain the smallest possible wall diameter, while at the same timeproviding suitable radial support to the sheath. An outer tube is formedof a composition, such as a polyether block amide or a polyamide(nylon), that provides sufficient flexibility to the sheath so that itcan bend along the tortuous passageways.

The medical interventional device, such as an expandable stent, etc., isdelivered to the target site from a lumen in the introducer sheath.Typically, the device is deployed at the target site by withdrawing theintroducer sheath from around the stent while the stent is in aconstricted condition. An inner catheter may be provided in the sheathlumen for preventing the stent from withdrawing with the sheath. In analternative arrangement, the constricted stent may be pushed from thedistal end of the sheath by a pusher mechanism positioned in the sheathlumen. In either technique, upon deployment from the sheath at thetarget site, the device expands to the diameter of the surrounding bodypassageway.

Deployment of expandable medical interventional devices, such as stents,in this manner is now a routine practice, and such deployment is oftencarried out with only a minimum of complications, if any. This isparticularly true when such devices have a relatively short length(e.g., less than about 80 mm) and/or a relatively modest outer diameter.However, as medical technology has progressed, stents and otherinterventional devices having longer lengths (e.g., about 100 to 300 mmor more) and/or having outer coatings, coverings, etc., that increasethe effective outer diameter of the stent have become more common. Whensuch stents are placed in a sheath lumen for delivery to the targetsite, the greater length and/or outer diameter of the stent increasesthe deployment forces necessary to extract the stent from the sheathwhen compared to shorter and/or lesser diameter stents. This increase indeployment forces is due primarily to the increased radiallyoutwardly-directed forces exerted by the longer and/or greater diameterstents on the interior wall of the sheath.

In this event, an introducer sheath having a coiled reinforcement asdescribed above has a tendency to stretch longitudinally as it iswithdrawn from around the interventional device. Although thisphenomenon may occur on some occasions with non-coated, non-covered, orshorter interventional devices, it is more pronounced with the coated,covered, or longer diameter devices that exert increased deploymentforces on the interior wall of the sheath. With such coated, covered, orlonger diameter devices, the stretching of the sheath causes thedistance between adjacent turns of the coil to increase. Thislongitudinal expansion of the reinforcing coil adversely affects theability of the sheath wall to withstand the radial expansive forcesexerted on the interior of the wall by the stent, which can result inthe formation of pockets along the wall of the sheath between adjacentcoil turns. When this occurs, surfaces of the undeployed stent mayexpand into such pockets, thereby undesirably increasing the resistanceimparted by the stent upon the sheath, and hindering efficientdeployment of the stent. In addition, the sheath may elongate as it iswithdrawn from the stent. When such elongation occurs, the distance thesheath handle travels is reduced, which may prevent the stent from beingfully deployed in the vessel from the sheath.

It is desired to provide an improved introducer sheath or other medicalapparatus suitable for traversing tortuous passageways in the patient'sanatomy during deployment of a medical interventional device, such as anexpandable stent. More particularly, it is desired to provide animproved introducer sheath that is capable of efficiently deployinginterventional devices that exert high radial forces on the sheathduring deployment.

SUMMARY

The problems of the prior art are addressed by the introducer sheath ofthe present invention. In one form thereof, the introducer sheathincludes an inner liner having a passageway extending longitudinallytherethrough. A reinforcing member comprising a coil having adjacentcoil turns is positioned longitudinally over the inner liner. Each coilturn has a cross-section comprising opposing end portions and a centerportion, wherein a thickness of the coil turns at the end portions isgreater than a thickness at the center portion. An outer jacket ispositioned longitudinally over the inner liner and the coil, and isbonded to the inner liner between the coil turns.

In another form thereof, the invention comprises an introducer sheath.The introducer sheath includes an inner liner having a passagewayextending longitudinally therethrough. A coil having adjacent coil turnsis positioned longitudinally over the inner liner. Each of the coilturns has a cross-section comprising opposing end portions, and a centerportion disposed between the opposing end portions. The center portionhas a thickness not exceeding about one-third of a thickness of the endportions for reducing a bending modulus of the coil, and the endportions have a generally curved outer surface. An outer jacket ispositioned longitudinally over the inner liner and the coil. The outerjacket is bonded to the inner liner between the coil turns. At least adistal end portion of the outer jacket has a durometer between about 70and 90 on the Shore D scale.

In still another form thereof, the invention comprises a method forforming an introducer sheath. An inner liner is positioned over amandrel. A coil having adjacent coil turns is positioned longitudinallyover the inner liner. Each of the coil turns has a cross-sectioncomprising opposing end portions and a center portion disposed betweenthe opposing end portions, wherein the end portions have a greaterthickness than a thickness of the center portion. A polymeric outerjacket is positioned longitudinally over the inner liner and the coil.An assembly comprising the mandrel, inner liner, reinforcing member andouter jacket is exposed to sufficient heat to at least partially meltthe outer jacket such that a melted portion of said outer jacket flowsbetween the coil turns and bonds to an outer surface of the inner liner.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of an introducer sheath according to an embodimentof the present invention;

FIG. 2 is a longitudinal cross-sectional view of a segment of theintroducer sheath, taken along line 2-2 of FIG. 1;

FIG. 2A is a cross-sectional view of a coil turn from the sheath of FIG.2, removed from the remaining elements of the sheath;

FIG. 2B is an enlarged view of coil end 41 of FIG. 2A;

FIG. 2C is a cross-sectional view of an alternative coil turn profile;

FIG. 3 is a longitudinal cross-sectional view of a prior art sheath; and

FIG. 3A is a cross-sectional view of a coil turn from the prior artsheath of FIG. 3, removed from the remaining elements of the sheath.

DETAILED DESCRIPTION OF THE DRAWINGS AND THE PRESENTLY PREFERREDEMBODIMENTS

For the purposes of promoting an understanding of the principles of theinvention, reference will now be made to the embodiments illustrated inthe drawings, and specific language will be used to describe the same.It should nevertheless be understood that no limitation of the scope ofthe invention is thereby intended, such alterations and furthermodifications in the illustrated device, and such further applicationsof the principles of the invention as illustrated therein beingcontemplated as would normally occur to one skilled in the art to whichthe invention relates.

In the following discussion, the terms “proximal” and “distal” will beused to describe the opposing axial ends of the sheath, as well as theaxial ends of component features of the sheath. The term “proximal” isused in its conventional sense to refer to the end of the sheath (orcomponent thereof) that is closest to the operator during use of thedevice. The term “distal” is used in its conventional sense to refer tothe end of the sheath (or component thereof) that is initially insertedinto the patient, or that is closest to the patient during use.

When conventional introducer sheaths are used to deploy medicalinterventional devices, such as stents, having a relatively shortlength, such deployments may often be carried out without unduecomplication. Typically, the stent is nested, or housed, in the distalportion of the sheath in a radially compressed condition. As the stentis deployed from the distal end of the sheath, the stent radiallyexpands to the diameter of the body passageway in which it has beenpositioned. The relatively short length of the stent, most of which areless than about 80 mm in length, typically provides minimal resistanceto the interior of the sheath as the compressed sheath is deployedtherefrom.

When comparatively longer stents (e.g., stents greater than about 100 mmin length, and especially, stents greater than about 140 mm in length)are deployed from prior art sheaths, however, the deployment of thestent from a sheath may be less than optimal. Due to the greater lengthof these stents, a greater aggregate outward force is exerted by thecompressed stent upon the interior wall of the sheath, when compared tothe force exerted by a stent of a lesser length. As a result, a higherpush force must typically be imparted by the inner catheter to overcomethe tendency of the stent to remain with the sheath as the sheath iswithdrawn from the passageway. A high push force as described may alsobe required upon deployment of coated or covered stents of any lengthfrom the sheath. This is due to the increased forces exerted against thewall of the sheath by the larger diameter coated or covered stent whencompared to an otherwise similar, but uncoated or uncovered stent.

The forces exerted by the compressed stent upon the interior wall of thesheath upon deployment may cause the sheath to stretch, or elongate, inthe longitudinal direction as the sheath is withdrawn from around thestent. Stretching may have little practical significance when smallerstents are positioned within the sheath. However, as stated above, suchstretching can become problematic with larger stents and/or with coatedor covered stents, such that in some cases, the stent cannot beefficiently deployed from the elongated sheath.

One way to address the problem of elongation of the sheath is toincrease the stiffness of the outer jacket material of the sheath. Asheath having a stiffer outer jacket has less propensity to stretch upondeployment of the stent when compared to one having a more flexibleouter jacket. As a result, the likelihood of deployment difficulties isminimized.

Although the use of the stiffer outer jacket addresses the problem ofsheath elongation as described, the flexibility of the overall sheath iscompromised when compared to an otherwise similar sheath having a moreflexible outer jacket. In addition, when the stiff sheath also includesa flat wire coil, the sheath has an increased likelihood of crackingupon bending as the sheath traverses a curved passageway in the body ofthe patient. This increased likelihood of cracking is believed due, atleast in part, to the presence of the defined edges present at each ofthe corners of the flat wire coil, and to the concentration of mass atthe interior center of the flat wire.

FIG. 1 illustrates a side view of an introducer sheath 10 according toan embodiment of the present invention. Introducer sheath 10 includes anouter tube 12, having a distal portion 13 and a proximal portion 15.Preferably, distal portion 13 tapers to a tapered distal end 14. Aninner passageway 16 extends through sheath 10 in well-known fashion.

In FIG. 1, sheath 10 is shown in combination with an optional dilator,or inner catheter, 18 and a connector hub 22. Dilators, inner catheters,and connector hubs for use with introducer devices, such as sheath 10,are well known in the art, and the elements illustrated in FIG. 1 may bereplaced with various other elements known in the art. As shown herein,inner catheter 18 extends longitudinally through the passageway of thesheath. The inner catheter includes a tapered distal end 19 foraccessing and dilating an access site, typically over a wire guide (notshown), by any conventional access technique, such as the well-knownSeldinger technique. A Luer lock connector 20 may be attached at theproximal end of the inner catheter for connection to a syringe or othermedical apparatus in well-known fashion.

Optional connector hub 22 is attached about the proximal end of thesheath during use. Connector hub 22 may include one or more conventionalvalve members, such as disk valves (not shown), for preventing thebackflow of fluids therethrough. Connector hub 22 may also include aside arm 23, to which a polymeric tube 24 and a conventional connector25 may be connected for introducing and aspirating fluids therethroughin well-known fashion.

FIG. 2 is an enlarged longitudinal cross-sectional view of a segment ofintroducer sheath 10 of FIG. 1. This figure illustrates the layeredstructure of the sheath wall. The view of introducer sheath 10 depictedin FIG. 2 does not include the optional inner catheter 18 disposed inpassageway 16, as shown in FIG. 1. As illustrated, sheath 10 comprisesan inner liner 30, having a radially outer surface 32 and a radiallyinner surface 33. A reinforcing member, i.e., coil 40, is wound orotherwise fitted around outer surface 32 of the inner liner. A polymericouter layer or jacket 50 is bonded to the outer surface 32 of innerliner 30 through the spaced turns of the coil 40. The cross-sectionalprofile of coil 40 is further described hereinbelow.

Inner liner 30 is typically formed of a lubricious material. Preferably,the lubricious material comprises a fluoropolymer, such as PTFE or FEP.Lubricious liners for sheaths are well known in the medical arts, andthose skilled in the art can readily select an appropriate liner for aparticular use. The lubricious material provides a slippery, lowfriction inner surface 33 to ease insertion and/or withdrawal throughpassageway 16 of the inner catheter and/or a medical interventionaldevice, such as a stent. Inner liner 30 preferably has a substantiallyuniform inner diameter that extends the entire length of passageway 16,to allow passage therethrough of an interventional device having thelargest possible diameter. The radially outer surface 32 of liner 30 maybe roughened in any conventional manner, such as by machine grinding orchemical etching, to form an irregular surface to facilitate bondingwith outer jacket 50. The wall of the liner will also preferably havesufficient structural integrity to prevent the outer jacket and/or coilturns from protruding into inner passageway 16.

Outer jacket 50 may generally be formed from any composition commonlyused for such purposes in a medical device. Preferably, outer jacket 50comprises a heat formable polymeric material capable of forming a securebond with inner liner 30, and more preferably, with a roughened outersurface 32 of the liner. Non-limiting examples of suitable compositionsinclude a polyether block amide, a polyamide (nylon), a polyurethane,and like compositions capable of securely bonding, adhering, orotherwise securely engaging inner liner 30. In many cases it ispreferred to form outer jacket 50 from a material having a lower melttemperature than that of liner 30. To this end, the outer jacket can beheated at a temperature suitable to melt the jacket to facilitatebonding with the inner liner. When the heat formable material melts,portions flow between the respective turns of the coil, and bond to theouter surface 33 of the inner liner.

The outer jacket composition is formulated to have a durometer thatprovides sufficient flexibility to enable the sheath to bend through thedesired body pathway. In some instances, the outer jacket may have adurometer of a range commonly provided in sheaths used to deploy medicalinterventional devices. One very common durometer range that may besuitable in many such instances is about 55 to 65 on the Shore D scale.However, as stated above, in order to address problems such as sheathelongation that may be encountered upon deployment of an elongatedinterventional device and/or a coated or covered interventional device,it may be desirable to utilize an outer jacket formed of a compositionhaving a higher durometer, or in other words, that is stiffer than ajacket formulated to have the conventional durometer range describedabove.

One particular outer jacket composition that may be utilized with theprofiled reinforcing member described herein is a composition having adurometer between about 70 and 100 on the Shore D scale. Preferably, thedurometer is between about 70 and 90, and more preferably about 80 onthe Shore D scale. Such a composition provides an outer jacket having agreater stiffness than commonly provided in such sheaths. When aconventional sheath of a type described above having an outer jacketdurometer between about 55 and 65 on the Shore D scale is utilized todeploy a stent or other interventional device that has a greater lengthand/or outer diameter than normal, the distal portion of the sheathhaving the stent nested therein may have insufficient radial rigidity toadequately withstand the outwardly-directed forces exerted by thecompressed stent on the interior wall of the sheath.

By increasing the stiffness (i.e., durometer) of at least the distalportion of the outer jacket, that is, the portion of the sheath thathouses the stent, this sheath portion has a greater ability to withstandthe radially outwardly-directed forces exerted by the stent, whencompared to a sheath having a more flexible distal portion. Althoughother portions of the sheath outer jacket may also be formed from a highdurometer material as described above, it is desired that at least thedistal portion of the sheath that houses the stent (e.g., thedistal-most 1-30 cm of the sheath) have such durometer.

The reinforcing member, such as coil 40, of sheath 10 may be formed frommaterials known for such use in the medical arts. Non-limiting examplesof such materials include metals, metal alloys (e.g., stainless steel ora shape memory composition such as nitinol), and composite materials. Ifdesired, the coil 40 may extend the entire length of sheath 10. However,it is generally preferred that the coil terminate short of the proximaland distal ends of the sheath in well-known fashion. Terminating thecoil short of the distal end facilitates the ability to form a desiredconfiguration (e.g., a distal taper) at the non-reinforced distal end.Terminating short of the proximal end facilitates flaring of that end.

Conventionally, the reinforcing coil of an introducer sheath was formedfrom flat wire having a generally rectangular cross-section. See, e.g.,FIGS. 3 and 3A. FIG. 3 illustrates a prior art sheath 80 having flatwire coil 90. Sheath 80 includes an inner liner 82 and an outer jacket86 as before. Flat wire coil 90 has a rectangular cross-section, andincludes four squared edges 91, 92, 93, 94, as best shown in FIG. 3A.Providing a sheath having a flat wire coil enables the sheath tomaintain the smallest possible wall diameter, while at the same timeproviding suitable radial support to the sheath.

With a sheath having a conventional outer jacket durometer, e.g., about55-65 or less on the Shore D scale, the sheath having a flat wire coilis generally able to bend about most body pathways without cracking.However, when it is desired to provide a sheath having an outer jacketof a higher durometer (e.g., 70 to 90 or higher on the Shore D scale)than provided in the more conventional sheaths, the stiffer outer jacketmaterial has an increased propensity to crack upon bending of thesheath.

The coil utilized in the sheath described herein is configured in amanner to reduce the likelihood that the outer jacket of the sheath willcrack upon bending. One form of a coil 40 utilized in sheath 10 isillustrated in FIGS. 2, 2A, and 2B. As shown in the figures, the mass atthe center portion 43 of the wire cross section is reduced when comparedto conventional flat wire of the type shown in FIGS. 3, 3A. The dottedlines in FIGS. 2A, 2B are provided to mimic the mass that wouldotherwise be present at the center portion of a conventional flat wire.Reducing the thickness at the center of the wire cross section whencompared to the end portions decreases the bending modulus of the wire.This improves the overall flexibility of the wire, and therefore, of thesheath. If the overall thickness of the entire wire was reduced, ratherthan the center portion as described, the radial support provided by thecoil would be adversely affected. By maintaining the mass at the endportions 41, 42 as described, the coil provides a suitable level ofradial support to the sheath, notwithstanding the reduced thickness atthe center portion.

Those skilled in the art will appreciate that varying amounts of massmay be reduced in a particular application. In some applications whereinmaximum sheath flexibility may not be required, lesser amounts of massmay be removed when compared to an application in which maximal sheathflexibility is desired. In general, as the thickness of the area removedincreases, there is an increase in flexibility of the sheath. Optimally,the amount of mass removed would approach one-half of the thickness “t”of the wire, leaving only a sufficient amount of mass to connect the twowire ends 41, 42. Generally, it is preferred to remove up to aboutone-third (“t1”) of the thickness of the wire from either surface of thewire (FIG. 2B). This is believed in most applications to impart asufficient decrease in the bending modulus of the wire to providesuitable wire flexibility, while at the same time maintaining structuralintegrity of the wire. Those skilled in the art will appreciate that insome applications somewhat greater amounts, e.g., up to about 40-45%, ofthe thickness of the wire from each surface may be removed to providemaximal bending. Similarly, in instances in which less bending isexpected, lesser amounts of wire, e.g., between about 10 and 30%, may beremoved from each surface.

Although it is preferred to remove equal amounts of mass from eachsurface as described and as shown in the figures, this may not berequired in all instances. Thus, in some applications, different amountsof mass may be removed from the respective upper and lower surfaces ofthe wire. As a further alternative, in some applications, suitablebending may be achieved by removing mass from only one surface of thewire, and leaving the other surface intact.

In addition to removing mass from the center portion of the wire asdescribed, it is preferred to provide a reinforcing wire having curved,or rounded, wire ends. See, e.g., wire ends 41, 42, in FIGS. 2, 2A, 2B.By rounding the outer edges of the wire, the stress concentrations atthe wire edges are reduced when compared to the stress concentrations atthe edges of a conventional flat wire coil, such as squared edges 91-94of conventional flat wire coil 90. Reducing the stress concentration atthe edges of a wire further reduces the likelihood that the sheath willcrack along one or more edges upon bending, or kinking, of the sheath asit traverses a curved body pathway. One way to quantify an amount ofcurvature in a preferred arrangement is described by the formula“r=t/2”, wherein “r” is the radius of the coil end (e.g., end 41 or 42)and “t” is the thickness of the wire (FIG. 2B). Although an amount ofcurvature defined by the formula recited above is preferred for mostapplications, the skilled artisan may determine that a lesser amount ofcurvature (e.g., r=t/4, r=t/8, or r=t/16) may be suitable for aparticular application. Those skilled in the art will recognize that asthe denominator increases, the radius at the edges is decreasing. It isbelieved that a skilled artisan can readily determine a suitable degreeof curvature for a particular application when applying the teachings ofthe present disclosure.

Although coil 40 as shown in the figures includes the preferredarrangement of both rounded edges and a reduced mass center portion, thepresence of rounded edges may not be required in all embodiments.Rather, the decrease in bending modulus provided by the reduced masscenter portion may in some instances improve the flexibility of thesheath to such an extent that rounding of the edges is unnecessary.However, it is believed preferable to include both rounded edges and areduced mass center portion. In this instance, the artisan need notseparately consider whether the presence of sharp edges is adverse tothe functioning of the sheath in the particular application.Furthermore, it simplifies manufacturing techniques to construct suchsheaths from a common wire configuration.

The cross-sectional profile of the coil need not be exactly as shown inFIG. 2A. As stated, it is desired to reduce the mass at the center ofthe wire. Those skilled in the art recognize that other profiles wouldaccomplish the objective of minimizing the amount of mass at the centerof the wire. FIG. 2C illustrates one example of an alternativecross-sectional profile. In this case, relatively straight lines 44, 45extend from coil ends 41, 42 and meet at a center portion 46. Other wireconfigurations may be substituted for those shown in FIGS. 2A and 2C, aslong as sufficient mass is removed from the center of the wire todecrease the bending modulus of the wire such that the overallflexibility of the wire, and therefore, of the sheath, is enhanced.Although a certain amount of trial and error can be employed todetermine suitable dimensions and configurations for a wire that isprofiled in the general manner described herein, the skilled artisan canreadily create such a wire when proceeding in accordance with theteachings provided herein.

Those skilled in the art will appreciate that the profile of thereinforcing member and/or the stiffness of an outer jacket compositionmay vary in a particular sheath depending upon factors such as the bodypathway to be traversed, and the length and/or diameter of theinterventional device to be deployed from the sheath. It is believedthat a skilled artisan can readily determine a suitable combination offactors to achieve a sufficient amount of flexibility of the sheath fora particular application when applying the teachings provided herein.

Coils having a profile as described herein may be readily prepared byknown techniques. For example, a conventional flat wire can be drawnthrough a die having the desired configuration. Alternatively, roundwire can be drawn down through a series of well-known steps to impartthe desired profile in the wire. Once a wire having the desired profileis formed, the wire may then be coiled using a conventional coilingmachine in the same fashion as flat wire is presently coiled in a sheathof the type described herein.

One method of forming the sheath 10 will now be described. Initially,the inner liner 30 is positioned along a suitably-sized mandrel.Generally, the mandrel will have an outer diameter substantially thesame as the inner diameter of the inner liner to insure a closetolerance between the two. The profiled coil 40 is then positioned overthe inner liner and mandrel by any conventional technique, and thetubular outer jacket 50 is positioned over the mandrel, liner and coil.The entire assembly is placed in a suitable heat shrink enclosure. Heatshrink enclosures for use in forming medical devices are well known inthe art. Fluorinated ethylene propylene (FEP) is a particularlypreferred composition for use herein as a heat shrink enclosure. Thoseskilled in the art will appreciate that various alternative compositionsfor the heat shrink enclosure are also suitable for use in forming thissheath, as long as the melt temperature of the material used for theouter jacket is lower than that of the heat shrink enclosure.

The heat shrink enclosure and contents are placed in an oven and baked(typically at about 385° F. (196° C.) when FEP is used as the heatshrink and a polyether block amide is used as an outer jacket material)for a suitable period of time to melt the outer jacket material suchthat it flows between the coil turns as described and bonds with theouter surface of the inner liner. After removal from the oven, theentire assembly is cooled, the FEP enclosure is cut away, and themandrel is removed.

Additional details of the construction or composition of the variouselements of sheath 10 not otherwise disclosed are not believed to becritical to the present invention, so long as the recited elementspossess the strength and/or physical properties to enable them toperform as required. Many such details not described herein are recitedin detail in the incorporated-by-reference U.S. Pat. No. 5,380,304, andU.S. Patent Publication No. 2001/0034514.

It is therefore intended that the foregoing detailed description beregarded as illustrative rather than limiting, and that it be understoodthat it is the following claims, including all equivalents, that areintended to define the spirit and scope of this invention.

1. An introducer sheath comprising: an inner liner having a passagewayextending longitudinally therethrough; a reinforcing member positionedlongitudinally over the inner liner, the reinforcing member comprising acoil having adjacent coil turns, each of said coil turns having across-section comprising opposing end portions and a center portion,wherein a thickness of said coil turns at said end portions is greaterthan a thickness at said center portion; and an outer jacket positionedlongitudinally over said inner liner and said coil, said outer jacketbonded to said inner liner between said coil turns.
 2. The introducersheath of claim 1, wherein at least a distal end portion of the outerjacket has a durometer between about 70 and 90 on the Shore D scale. 3.The introducer sheath of claim 1, wherein said thickness of said coilturn center portion does not exceed about one-third of said thickness ofsaid end portions.
 4. The introducer sheath of claim 1, wherein saidcoil turn cross-section has an upper and lower surface, and wherein upto about 40% of said coil turn thickness is removed from said centerportion at each of said upper and lower surfaces when compared to thethickness of said end portions.
 5. The introducer sheath of claim 1,wherein said coil turn cross-section has an upper and lower surface, andwherein between about 10 and 30% of said coil turn thickness is removedfrom said center portion of at least one of said upper and lowersurfaces.
 6. The introducer sheath of claim 1, wherein said end portionshave a generally curved outer surface.
 7. The introducer sheath of claim6, wherein at least one of said coil end portions has a radius r and athickness t, said end portion generally curved surface being defined bythe formula r=t/2.
 8. The introducer sheath of claim 6, wherein at leastone of said coil end portions has a radius r and a thickness t, said endportion generally curved surface not exceeding r=t/4.
 9. The introducersheath of claim 1, wherein at least a distal end portion of the outerjacket has a durometer between about 70 and 90 on the Shore D scale,wherein the thickness of the center portion is about one-third of thethickness of the end portions, and wherein said end portions have agenerally curved outer surface.
 10. The introducer sheath of claim 1,wherein the thickness of the coil turn center portion is about one-thirdof the thickness of the end portions.
 11. The introducer sheath of claim1, wherein said inner liner comprises a lubricious fluoropolymer, andsaid outer jacket comprises at least one of a polyether block amide, apolyamide, and a polyurethane.
 12. An introducer sheath comprising: aninner liner having a passageway extending longitudinally therethrough,said inner liner having an outer surface; a coil positionedlongitudinally over the inner liner, the coil having adjacent coilturns, each of said coil turns having a cross-section comprisingopposing end portions and a center portion disposed between saidopposing end portions, said center portion having a thickness notexceeding about one-third of a thickness of said end portions forreducing a bending modulus of said coil, said end portions having agenerally curved outer surface; and an outer jacket positionedlongitudinally over said inner liner and said coil, said outer jacketbonded to said inner liner between said coil turns, at least a distalend portion of the outer jacket having a durometer between about 70 and90 on the Shore D scale.
 13. The introducer sheath of claim 12, whereinat least one of said coil end portions has a radius r and a thickness t,said end portion generally curved surface being defined by the formular=t/2.
 14. The introducer sheath of claim 12, wherein at least one ofsaid coil end portions has a radius r and a thickness t, said endportion generally curved surface not exceeding r=t/4.
 15. The introducersheath of claim 12, wherein said coil turn cross-section comprises aboutone-third of said thickness of said end portions.
 16. A method forforming an introducer sheath, comprising: positioning an inner linerover a mandrel, the inner liner having a passageway extendingtherethrough, and having an outer surface; positioning a reinforcingmember longitudinally over the inner liner, the reinforcing membercomprising a coil having adjacent coil turns, each of said coil turnshaving a cross-section comprising opposing end portions and a centerportion disposed between said opposing end portions, said end portionshaving a greater thickness than a thickness of said center portion;positioning a polymeric outer jacket longitudinally over said innerliner and said coil; and exposing an assembly comprising the mandrel,inner liner, reinforcing member and outer jacket to sufficient heat toat least partially melt the outer jacket such that a melted portion ofsaid outer jacket flows between said coil turns and bonds to an outersurface of said inner liner.
 17. The method of claim 16, wherein saidcoil turn cross-section has an upper and lower surface, and wherein upto about 40% of said coil turn thickness is removed from said centerportion at each of said upper and lower surfaces when compared to thethickness of said end portions.
 18. The method of claim 16, wherein saidcoil turn cross-section has an upper and lower surface, and whereinbetween about 10 and 30% of said coil turn thickness is removed fromsaid center portion of at least one of said upper and lower surfaces.19. The method of claim 16, wherein said coil end portions have agenerally curved outer surface, and wherein the thickness of the coilturn center portion is about one-third of the thickness of the endportions.
 20. The method of claim 19, wherein said inner liner comprisesa lubricious fluoropolymer having a roughened outer surface, and saidouter jacket comprises at least one of a polyether block amide, apolyamide, and a polyurethane, and wherein at least a distal end portionof the outer jacket has a durometer between about 70 and 90 on the ShoreD scale.